Antagonism to muscarinic receptors is known to cause bronchodilation, gastrointestinal hypanakinesis, gastric hyposecretion, dry mouth, mydriasis, suppression of bladder contraction, hypohidrosis, tachycardia and the like ["Basic and Clinical Pharmacology", 4th ed., APPLETON & LANGE, pp. 83-92 (1989); Drug News & Perspective, 5(6), pp. 345-352 (1992)].
It has been made clear through recent studies that there are at least three subtypes of muscarinic receptors; the M.sub.1 receptors being present mainly in the brain, the M.sub.2 receptors mainly in the heart, and the M.sub.3 receptors, on smooth muscles and glandular tissues. However, all of the large number of compounds heretofore known to exhibit antagonism to muscarinic receptors non-selectively antagonize the three subtypes of muscarinic receptors. Consequently, attempts to use these compounds as therapeutic or prophylactic agents for diseases of the respiratory system have caused undesirable side effects such as dry mouth, nausea and mydriasis. Still in addition, particularly serious side effects associated with the central nervous system, such as dementia, attributable to the M.sub.1 receptors and those associated with the heart, such as tachycardia mediated by the M.sub.2 receptors, pose problems, and their solution is strongly demanded.
Chemical compounds structurally similar to those of the present invention include, for instance, the compounds cited as Example 33 in the International Patent Publication WO 93/16048. The publication also discloses that the compounds exhibit anticholinergic activity. However, the compounds according to this invention are neither specifically disclosed nor suggested. Nor is there any mention at all of highly selective antagonism to muscarine M.sub.3 receptors.